plague

• plague is a bacterial infection
• organism that causes the plague

  Yersinia pestis
• modes of transmission of plague

  flea bite, human to human
• different forms of plague

  bubonic, pneumonic and septicaemic
• Yersinia pestis

  • rod shaped bacteria
  • can survive in aerobic and anaerobic environments
  • gram negative
• Yersinia pestis main habitats

  gut of flea, blood/tissue of mammalian host
• sylvatic cycle is 


  between fleas and wild rodents
• urban cycle is 


  between fleas and domestic rodents
• link between wild and domestic is

  brown rat
• wild and domestic are chief reservoirs for plague
• 2500 species of fleas, 80 found to be infected with Y.pestis
• vector efficiency could be due to

  • insect immunity
  • midgut digestive enzymes
  • frequency of feeding and defecation
  • flea life span after infection
• transmission by flea

  • vector infected following uptake of blood
  • pathogen replicates and disseminates in vector
  • Y.pestis in flea digestive tract, transmitted by regurgitation
• Yersinia pestis in flea persistence depends on

  • formation of multicellular aggregates
  • ability to form biofilm, creating blockage in proventriculus
• blockage of proventricular valve causes regurgitative transmission
• pathogenicity in humans

  • local lesion and inflammation of human
  • toxins produced by Yersinia pestis cause most harm, endothelial damage and necrosis
  • Yersinia pestis surrounded by F1 capsule as grows, no phagocytosis
  • Yersinia pestis injects effector proteins into neutrophils to kill them
  • Yersinia pestis not killed by macrophage, can be phagocytosed, then toxins damage from inside
• 3 major plague pandemics in history
• 3 plagues

  • justinianic plague
  • black death
  • modern plague
• Yersinia pestis to talk about plagues
• biological welfare

  • widespread availabilty around the world
  • capacity for mass production
  • high fatality rate
  • rapid secondary spread potential
• symptoms

  • flu-like
  • fever
  • chills
  • head and body ache
  • weakness
  • vomiting
• bubonic plague

  • most common form
  • spread via lymphatic system (to lymph nodes)
  • lymph nodes swell (form buboes)
  • buboes may burst to form open sores
  • mortality rate 50-60% (untreated)
• septicaemic plague (black death)

  • blood poisoning
  • result from flea bite, or direct contact
  • bubonic plague can develop into secondary septicaemic plague
  • can cause meningitis, endotoxic shock and disseminated intravascular coagulation
  • mortality if untreated 100%
• pneumonic plague

  • least common
  • most virulent
  • caused by infection spreading to lungs, in advanced bubonic plague
  • causes acute pulmonary insufficiency, sepsis and toxic shock
• transmission (flea bite)


  most common, results in primary bubonic or septicaemic plague
• transmission (contaminated fluid or tissue)


  results in bubonic or septicaemic plague
• transmission (infectious droplets)


  pneumonic plague sufferer coughs, giving another pneumonic plague is breathed in
• WHO estimates plague aerosols remain effective and infectious for

  an hour
• diagnosis can be from

  lymph nodes, blood, sputum, bronchial/tracheal washing
• can be treated with antibiotics if given early
• antibiotics such as 


  streptomycin, tetracycline, chloramphenicol
• pneumonic plague can be fatal 18-24 hours of disease onset
• quarantine to isolate infected
• vaccines are based on formaldehyde inactivated whole cells
• vaccine gives partial protection
• Yersinia has up to 17 different species
• gene gain and loss are major drivers of bacterial evolution
• Y.pestis didn't used to be flea-borne